JP6461248B2 - Aluminum alloy foil and method for producing aluminum alloy foil - Google Patents

Description

  The present invention relates to an aluminum alloy foil excellent in formability and a method for producing the aluminum alloy foil.

Aluminum alloy foils used for packaging materials such as foods and lithium ion batteries are required to have high elongation because they are molded by being greatly deformed by press molding or the like. Conventionally, as a material having high elongation, for example, a JIS A1000 alloy called 1N30 or the like, or a soft foil of JIS A8000 alloy such as 8079 or 8021 is used.
Aluminum alloy foils are not deformed in one direction, but are often so-called stretched and deformed in a plurality of directions. In addition, it is required that the elongation at 45 ° and 90 ° is also high with respect to the rolling direction. Recently, the foil as a packaging material has been made thinner in the field of battery packaging materials. Therefore, there is a demand for an aluminum alloy foil having high elongation even when the foil thickness is thin.

In order to realize an aluminum alloy foil having a high elongation, it has been proposed to control crystal grains in the alloy.
For example, in Patent Document 1, the number density of an intermetallic compound having an average crystal grain size of 20 μm or less and an equivalent circle diameter of 1.0 to 5.0 μm is set to a predetermined amount or more, whereby the intermetallic compound is recrystallized. The crystal grain size after the final annealing is made fine.
In Patent Document 2, a boundary having an orientation difference of 5 ° or more is defined as a crystal grain boundary in crystal orientation analysis by electron backscatter analysis image method (EBSD), and the crystal grains included in the crystal grain boundary are An aluminum alloy foil has been proposed in which the average value D is 12 μm or less and the area ratio of crystal grains having a crystal grain size exceeding 20 μm is 30% or less.
In Patent Document 3, the average crystal grain size and the average grain size of subgrains are defined to be not more than a predetermined value, and the dispersion density of the Al—Fe compound is defined to be not less than a predetermined value.

International Publication No. 2014/021170 International Publication No. 2014/034240 JP 2004-27353 A

However, the invention described in Patent Document 1 has a concern that the amount of Cu added is as large as 0.5 mass% at the maximum. Since Cu is an element that lowers the rollability even in a small amount, there is a risk that edge cracks occur during rolling and the foil breaks. Also, the average crystal grain size is large, and it may be difficult to maintain high formability when the thickness of the foil is reduced.
In Patent Document 2, a very fine crystal grain size is defined, but the crystal grain boundary is limited to those having an orientation difference of 5 ° or more. When the angle is 5 ° or more, a large-angle grain boundary and a small-angle grain boundary are mixed, and it is not certain whether the crystal grains surrounded by the large-angle grain boundary are fine.
Patent Document 3 is different from Documents 1 and 2 in that it is not a battery outer foil but a thin foil having a thickness of 10 μm or less, and is manufactured without intermediate annealing. Stable elongation cannot be obtained in the directions of °, 45 °, and 90 °. And an average crystal grain diameter is also 10 micrometers or more, and when the thickness of foil is thin, it cannot anticipate that a high moldability is obtained.

  The present invention has been made against the background of the above problems, and an object of the present invention is to provide an aluminum alloy foil having good workability and high elongation characteristics.

That is, the invention of the aluminum alloy foil of the first aspect of the present invention includes Fe: 1.0 mass% to 1.8 mass%, Si: 0.01 mass% to 0.10 mass%, Cu: 0.005 Containing not less than 0.05% by mass and not more than 0.05% by mass, Mn: regulated to not more than 0.01% by mass, and the balance is composed of Al and inevitable impurities,
In the crystal orientation analysis per unit area by backscattered electron diffraction, the average grain size is 5 μm or less and the maximum grain size / The average particle size ≦ 3.0, and the elongation in the 0 °, 45 °, and 90 ° directions with respect to the rolling direction when the thickness of the foil is 30 μm is 25% or more, respectively.

  The invention of the aluminum alloy foil of the second aspect of the present invention is characterized in that, in the first aspect of the present invention, in the crystal orientation analysis per unit area by backscattered electron diffraction, a grain boundary having a crystal orientation difference of 15 ° or more is greatly increased. A grain boundary having a tilt boundary and a crystal orientation difference of 2 ° or more and less than 15 ° is defined as a small tilt grain boundary, the length of the large tilt grain boundary is L1, and the length of the small tilt grain boundary is L2. In this case, L1 / L2> 2.0.

  A method for producing an aluminum alloy foil according to a third aspect of the present invention is a method for producing an aluminum alloy foil according to the first or second invention, wherein the aluminum alloy foil having the composition described in the first or second invention is used. The ingot is subjected to a homogenization treatment for 6 hours or more at 400 to 480 ° C., and after the homogenization treatment, hot rolling is performed so that a rolling finish temperature is 230 ° C. or more and less than 300 ° C. In the course of cold rolling, intermediate annealing at 300 ° C. to 400 ° C. is performed, and the final cold rolling rate after intermediate annealing is set to 92% or more.

The contents defined in the present invention will be described below.
Fe: 1.0% by mass or more and 1.8% by mass or less Fe is crystallized as an Al—Fe intermetallic compound at the time of casting. If the size of the compound is large, it becomes a recrystallization site at the time of annealing. There is an effect of refining crystal grains. When the Fe content is below the lower limit, the distribution density of coarse intermetallic compounds is lowered, the effect of miniaturization is low, and the final crystal grain size distribution is also nonuniform. When the content exceeds the upper limit, the effect of crystal grain refinement is saturated or reduced, and the size of the Al—Fe-based compound produced during casting becomes very large, and the elongation and rollability of the foil are lowered. For this reason, the content of Fe is set within the above range.
For the same reason, the lower limit of the Fe content is preferably 1.3% by mass and the upper limit is preferably 1.6% by mass.

Si: 0.01% by mass or more and 0.10% by mass or less Si forms an intermetallic compound together with Fe, but when the addition amount is large, the size of the compound becomes coarse and the distribution density decreases. When the content exceeds the upper limit, there is a concern that the rollability and elongation characteristics of the coarse crystallized product are deteriorated, and further, the uniformity of the recrystallized grain size distribution after the final annealing is lowered.
For these reasons, it is preferable that the Si content is low. However, if the content is less than 0.01% by mass, it is necessary to use a high-purity metal, and the manufacturing cost is greatly increased. Further, when a high-purity metal is used, trace components such as Cu are extremely low, so that excessive work softening occurs during cold rolling, and there is a concern that the rollability may be reduced. For the above reasons, the Si content is set within the above range.
For the same reason, the lower limit of the Si content is preferably 0.01% by mass and the upper limit is preferably 0.05% by mass.

Cu: 0.005 mass% or more and 0.05 mass% or less Cu is an element that increases the strength of the aluminum foil and decreases the elongation. On the other hand, there is an effect of suppressing excessive work softening during cold rolling. When the content is less than 0.005% by mass, the effect of suppressing the work softening is low, and when it exceeds 0.05% by mass, the elongation is clearly reduced. For this reason, content of Cu is made into the said range.
For the same reason, the lower limit of the Cu content is preferably 0.008 mass% and the upper limit is 0.012 mass%.

Mn: 0.01% by mass or less Mn dissolves in the aluminum matrix or / and forms a very fine compound and functions to suppress recrystallization of aluminum. If it is very small, suppression of work softening can be expected like Cu, but if it is added in a large amount, recrystallization during intermediate annealing and final annealing is delayed, and it becomes difficult to obtain fine and uniform crystal grains. . Therefore, the Mn content is restricted to 0.01% by mass or less.
For the same reason, the upper limit of the Mn content is more preferably 0.005% by mass. In addition, when positively suppressing the softening of processing, it is desirable to add 0.002% by mass or more of Mn.

-For crystal grains surrounded by a large tilt grain boundary with an orientation difference of 15 ° or more, the average grain size is 5 μm or less and the maximum grain size / average grain size ≦ 3.0
Since the soft aluminum foil has fine crystal grains, it can suppress the rough surface of the foil surface when deformed, and high elongation and high moldability associated therewith can be expected. Note that the influence of the crystal grain size increases as the foil thickness decreases. In order to realize high elongation characteristics and high formability associated therewith, it is desirable that the average crystal grain size is 5 μm or less with respect to the crystal grains surrounded by the large tilt grain boundaries having an orientation difference of 15 ° or more. However, even if the average crystal grain size is the same, if the grain size distribution of the crystal grains is not uniform, local deformation is likely to occur, and the elongation decreases. Therefore, not only the average crystal grain size is 5 μm or less, but also high elongation characteristics can be obtained by setting the maximum grain size / average grain size ≦ 3.0.
The average particle size is preferably 4.5 μm or less, and the ratio is preferably 2.0 or less.
A large-angle grain boundary map having an orientation difference of 15 ° or more can be obtained by analyzing crystal orientation per unit area by backscattered electron diffraction (EBSD).

・ Elongation in the direction of 0 °, 45 °, and 90 ° with respect to the rolling direction when the thickness of the foil is 30 μm is 25% or more respectively. For high formability, the elongation of the foil is important, and the direction parallel to the rolling direction is 0 in particular. It is important that the elongation is high in each direction of 0 °, 45 °, and 90 ° which is a normal direction of the rolling direction. Although the elongation value of the foil is greatly affected by the thickness of the foil, high moldability can be expected if the elongation is 25% or more at a thickness of 30 μm.

・ L1 / L2> 2.0 where L1 is the length of the large-angle grain boundary and L2 is the length of the low-angle grain boundary.
Although not limited to the Al—Fe alloy, depending on the recrystallization behavior during annealing, the length L1 of the large-angle grain boundary (HAGBs) and the length L2 of the small-angle grain boundary (LAGBs) occupying the total grain boundary. The ratio changes. When the ratio of LAGBs is high after the final annealing, even if the average crystal grains are fine, if L1 / L2 ≦ 2.0, local deformation is likely to occur and the elongation decreases. For this reason, it is desirable to satisfy L1 / L2> 2.0, and higher elongation can be expected by satisfying this rule. More preferably, the ratio is 2.5 or more.
The length of the large-angle grain boundary and the small-angle grain boundary can be measured by SEM-EBSD in the same manner as the crystal grain size. L1 / L2 is calculated from the total length of the large tilt grain boundary and the small tilt grain boundary in the observed visual field area.

-Homogenization treatment: Hold for 6 hours or more at 400-480 ° C The homogenization treatment here is aimed at eliminating micro segregation in the ingot and adjusting the distribution of intermetallic compounds. This is a very important process for obtaining a uniform grain structure. In the homogenization process, it is difficult to eliminate microsegregation in the ingot at a temperature lower than 400 ° C. Further, when the temperature exceeds 480 ° C., crystallized substances grow, and the density of coarse intermetallic compounds having a particle size of 1 μm or more and less than 3 μm, which become nucleation sites for recrystallization, is reduced, so that the crystal particle size tends to be coarse. In addition, homogenization treatment at a low temperature is effective for precipitating fine intermetallic compounds having a particle size of 0.1 μm or more and less than 1 μm at high density. When the temperature exceeds 480 ° C., the density of these fine intermetallic compounds is also high. It will decline. In a homogenization treatment at a low temperature of 480 ° C. or lower, a long-time heat treatment is required to precipitate these fine intermetallic compounds at a high density, and it is necessary to ensure a minimum of 6 hours or more. If it is less than 6 hours, the precipitation is not sufficient and the density of the fine intermetallic compound is lowered.

-Finishing temperature of hot rolling: 230 ° C or more and less than 300 ° C Hot rolling is performed after homogenization treatment. In hot rolling, it is desirable that the finishing temperature be less than 300 ° C. to suppress recrystallization. By setting the hot rolling finish temperature to less than 300 ° C., the hot rolled plate has a uniform fiber structure. By suppressing recrystallization after hot rolling in this way, the amount of strain accumulated up to the subsequent intermediate annealing plate thickness increases, and a fine recrystallized grain structure can be obtained during intermediate annealing. This leads to finer final crystal grains. When the temperature exceeds 300 ° C., recrystallization occurs in a part of the hot-rolled sheet, and the fiber structure and the recrystallized grain structure coexist. The recrystallized grain size during the intermediate annealing becomes non-uniform, which is the final This leads to non-uniform crystal grain size. In order to finish at less than 230 ° C., the temperature during hot rolling is also extremely low, so there is a concern that cracks occur on the side of the plate and the productivity is greatly reduced.

Intermediate annealing: 300 ° C to 400 ° C
Intermediate annealing softens the hardened material by repeating cold rolling to restore rollability, promotes precipitation of Fe, and lowers the amount of solid solution Fe. If the temperature is lower than 300 ° C., there is a risk that the recrystallization is not completed and the grain structure becomes non-uniform, and if the temperature is higher than 400 ° C., the recrystallized grains become coarse and the final crystal grain size becomes large. Furthermore, the precipitation amount of Fe falls at high temperature, and the amount of solid solution Fe increases. When the amount of solid solution Fe is large, recrystallization during the final annealing is suppressed, and the proportion of low-angle grain boundaries increases.

-Final cold rolling rate: 92% or more As the final cold rolling rate from the intermediate annealing to the final thickness is higher, the amount of strain accumulated in the material increases and the recrystallized grains after the final annealing become finer. In addition, since the crystal grains are refined even in the process of cold rolling (Grain Subvision), it is desirable that the final cold rolling rate is high in that sense as well. Specifically, the final cold rolling rate should be 92% or more. Desirably, if it is less than 92%, the amount of accumulated strain is reduced and the crystal grain refinement during rolling becomes insufficient, and the crystal grain size after final annealing becomes large. Also, the rate of in-situ recrystallization increases, LAGBs with an orientation difference of less than 15 ° increase, and HAGBs / LAGBs decrease. Although there is no demerit on the characteristics of the material with respect to the upper limit, producing a thin foil by cold rolling exceeding 99.9% leads to a decrease in rollability and there is a concern about an increase in fracture due to side cracks.

  According to the present invention, an aluminum alloy foil having high elongation characteristics can be obtained.

It is a figure which shows the planar shape of the square punch used in the limit shaping | molding height test in the Example of this invention.

The manufacturing method of the aluminum alloy foil of one Embodiment of this invention is demonstrated.
As an aluminum alloy, Fe: 1.0 mass% or more and 1.8 mass% or less, Si: 0.01 mass% or more and 0.10 mass% or less, Cu: 0.005 mass% or more and 0.05 mass% or less are contained Then, Mn was regulated to 0.01% by mass or less, and the balance was adjusted to a composition consisting of Al and other inevitable impurities to produce an aluminum alloy ingot. The method for producing the ingot is not particularly limited, and can be performed by a conventional method such as semi-continuous casting. The obtained ingot is subjected to a homogenization treatment that is held at 400 to 480 ° C. for 6 hours or more.

After the homogenization treatment, hot rolling is performed, and the rolling finish temperature is set to 230 ° C. or higher and lower than 300 ° C. Thereafter, cold rolling is performed, and intermediate annealing is performed during the cold rolling. In the intermediate annealing, the temperature is set to 300 ° C to 400 ° C. The intermediate annealing time is preferably 3 hours or more and less than 10 hours. If the annealing temperature is less than 3 hours, softening of the material may be insufficient when the annealing temperature is low, and long-term annealing for 10 hours or more is not economically preferable.
Cold rolling with intermediate annealing corresponds to final cold rolling, and the final cold rolling rate at that time is 92% or more. Although the thickness of foil is not specifically limited, For example, it can be set as 10 micrometers-40 micrometers.

The obtained aluminum alloy foil has excellent elongation characteristics. For example, when the thickness is 30 μm, the elongation in each direction of 0 °, 45 °, and 90 ° with respect to the rolling direction is 25% or more. Become.
In addition, in the crystal orientation analysis per unit area by backscattered electron diffraction (EBSD), the average grain size of a crystal grain surrounded by a large tilt grain boundary, which is a grain boundary having an orientation difference of 15 ° or more, is 5 μm or less and the maximum grain size The diameter / average particle diameter ≦ 3.0, and the crystal grains are fine. For this reason, the rough skin of the surface at the time of deform | transforming can be suppressed.
Further, in the crystal orientation analysis per unit area by backscattered electron diffraction (EBSD), a grain boundary having an orientation difference of 15 ° or more is defined as a grain boundary having an orientation difference of 2 ° or more and less than 15 °, and a large tilt boundary. When the length of the tilt grain boundary is L1, and the length of the small tilt grain boundary is L2, L1 / L2> 2.0. Thereby, higher elongation is realized.

In the aluminum alloy foil, it is desirable that the density of the intermetallic compound satisfies the following regulations.
-Density of Al-Fe-based intermetallic compound having a particle size of 1 μm or more and less than 3 μm: 1 × 10 ⁴ particles / mm ² or more A particle size of 1 μm or more is a particle size generally said to be a nucleation site during recrystallization In addition, since such an intermetallic compound is distributed at a high density, fine recrystallized grains can be easily obtained during annealing. If the particle size is less than 1 μm or the density is less than 1 × 10 ⁴ pieces / mm ² , it is difficult to work effectively as a nucleation site at the time of recrystallization, and if it exceeds 3 μm, it tends to lead to a reduction in pinholes and elongation during rolling. Become. For this reason, it is desirable that the density of the Al—Fe-based intermetallic compound having a particle size of 1 μm or more and less than 3 μm is within the above range.

-Density of Al-Fe-based intermetallic compound with a particle size of 0.1 μm or more and less than 1 μm: 2 × 10 ⁵ particles / mm ² or more Generally, it is a size that is said to be less likely to be a nucleation site during recrystallization, but crystal grains The result seems to have a great influence on the refining and recrystallization behavior. Although the overall picture of the mechanism is not yet clear, in addition to coarse intermetallic compounds having a particle size of 1 to 3 μm, fine crystals of less than 1 μm are present in a high density, so that recrystallized grains can be refined after final annealing, and HAGBs It has been confirmed that a decrease in the length of the length / LAGBs is suppressed. There is also a possibility of promoting the grain division (Grain subvision mechanism) during cold rolling. For this reason, it is desirable that the density of the Al—Fe-based intermetallic compound having a particle size of 0.1 μm or more and less than 1 μm is in the above range.

  The obtained aluminum alloy foil can be deformed by press molding or the like, and can be suitably used as food or a packaging material for lithium ion batteries. In addition, as this invention, the use of aluminum alloy foil is not limited above, It can utilize for an appropriate use.

An ingot of aluminum alloy having the composition shown in Table 1 was produced by a semi-continuous casting method. Then, for the obtained ingot, the production conditions shown in Table 1 (homogenization treatment conditions, hot rolling finish temperature, sheet thickness during intermediate annealing, intermediate annealing conditions, final cold rolling rate), Homogenization treatment, hot rolling, cold rolling, intermediate annealing, and cold rolling again were performed to produce an aluminum alloy foil.
The thickness of the foil was 30 μm.

The following measurements and evaluations were performed on the obtained aluminum alloy foil.
・ Tensile strength and elongation were both measured by a tensile test. The tensile test is based on JIS Z2241, and a JIS No. 5 test piece is taken from the sample so that the elongation in each direction of 0, 45, 90 ° with respect to the rolling direction can be measured. AGS-X 10 kN manufactured at a tensile rate of 2 mm / min. The calculation of the elongation rate is as follows. First, before the test, two lines are marked at the center of the test piece in the vertical direction of the test piece at an interval of 50 mm as a gauge distance. After testing, the fracture surface of the aluminum alloy foil was put together to measure the distance between marks, and the elongation (mm) obtained by subtracting the gauge distance (50 mm) from that was divided by the distance between gauge points (50 mm). (%) Was calculated.
Table 2 shows the measurement results of elongation (%) and tensile strength (MPa) in each direction.

・ Crystal grain size After electrolytic polishing of the foil surface, the crystal orientation analysis is performed by SEM (Scanning Electron Microscope) -EBSD, and the crystal grain boundary having an orientation difference between crystal grains of 15 ° or more is defined as HAGBs (high tilt grain boundary). And the size of the crystal grains surrounded by HAGBs was measured. Three fields of view size 45 × 90 μm were measured at a magnification of × 1000, and the average crystal grain size and the maximum grain size / average grain size were calculated. Each crystal grain size was calculated as a circle-equivalent diameter, and the average crystal grain size was calculated by using the EBSD Area method (Average by Area Fraction Method). For analysis, OSL Analysis from TSL Solutions was used.

・ HAGBs length / LAGBs length After electrolytic polishing of the foil surface, the crystal orientation analysis is performed by SEM-EBSD, and the high-angle grain boundaries (HAGBs) having an orientation difference between crystal grains of 15 ° or more and the orientation Small-angle grain boundaries (LAGBs) having a difference of 2 ° or more and less than 15 ° were observed. Three fields of view with a field size of 45 × 90 μm were measured at a magnification of 1000, the lengths of HAGBs and LAGBs in the field of view were determined, and the ratio was calculated. The calculated ratio is shown in Table 2 as HAGBs / LAGBs.

-Limit molding height The molding height was evaluated by a square tube molding test. The test is performed with a universal thin plate molding tester (Model 142/20 manufactured by ERICHSEN), and an aluminum foil having a thickness of 30 μm is formed into a square punch having a shape shown in FIG. 1 (length L = 37 mm on one side, chamfered corner) Diameter R = 4.5 mm). As test conditions, the wrinkle restraining force was 10 kN, the scale of the punch rising speed (molding speed) was 1, and mineral oil was applied as a lubricant on one side of the foil (the side on which the punch hits). Punch rising from the lower part of the device hits the foil, and the foil is molded. The maximum height of the punch that can be formed without cracks or pinholes after three consecutive moldings is the limit molding height of the material. (Mm). The height of the punch was changed at intervals of 0.5 mm.

-Density of intermetallic compound The intermetallic compound is obtained by cutting a parallel section (RD-ND plane) of a foil with a CP (Cross section polisher) and applying a field emission scanning electron microscope (FE-SEM: NV Zeiss manufactured by Carl Zeiss). And observed. For the “Al—Fe intermetallic compound having a particle diameter of 1 μm or more to less than 3 μm”, image analysis was performed on five visual fields observed at a magnification of × 2000, and the density was calculated. For “Al—Fe intermetallic compound having a particle size of 0.1 μm or more to less than 1 μm”, 10 fields observed at a magnification of 10000 × were subjected to image analysis, and the density was calculated. The calculation results are shown in Table 2.

  As shown in Table 2, in Examples 1 to 7 that satisfy the provisions of the present invention, good results were obtained in elongation, tensile strength, and limit overhang height, whereas In Comparative Examples 8 to 20 that did not satisfy any one or more, good results were not obtained.

Claims (3)

Fe: 1.0 to 1.8% by mass, Si: 0.01 to 0.10% by mass, Cu: 0.005 to 0.05% by mass, Mn: Controlled to 0.01% by mass or less, the balance has a composition consisting of Al and inevitable impurities
In the crystal orientation analysis per unit area by backscattered electron diffraction, the average grain size is 5 μm or less and the maximum grain size / An aluminum alloy foil characterized in that the average particle size ≦ 3.0 and the elongation in the 0 °, 45 °, and 90 ° directions with respect to the rolling direction when the thickness of the foil is 30 μm is 25% or more, respectively.   In a crystal orientation analysis per unit area by backscattered electron diffraction, a grain boundary having a crystal orientation difference of 15 ° or more is a high-angle grain boundary, and a crystal grain orientation difference is 2 ° or more and less than 15 °. L1 / L2> 2.0, where L1 is an average length of the large-angle grain boundary and L2 is an average length of the low-angle grain boundary. Item 2. The aluminum alloy foil according to Item 1. A method for producing the aluminum alloy foil according to claim 1 or 2,
The ingot of the aluminum alloy having the composition according to claim 1 or 2 is subjected to a homogenization treatment of holding at 400 to 480 ° C for 6 hours or more, and after the homogenization treatment, a rolling finish temperature is 230 ° C to 300 ° C. It is characterized by performing hot rolling to be less than ℃, performing intermediate annealing at 300 ℃ to 400 ℃ during the subsequent cold rolling, and setting the final cold rolling rate after intermediate annealing to 92% or more. A method for producing an aluminum alloy foil.

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